Sheaves are used to route a wireline from a reel to a stuffing box at a wellhead. One such sheave mounts onto the stuffing box and has a peripheral groove in which the wireline runs. Conventionally, the sheave's diameter and the depth of its groove are sized so that the center of the wireline will coincide with the centerline through the stuffing box. Therefore, a different sized sheave must be used to accommodate different sized wirelines so the wirelines can properly line up with the centerline of the stuffing box.
FIG. 1 shows one type of sheave assembly 10 according to the prior art for a stuffing box 20. This sheave assembly 10 and stuffing box 20 are manufactured by Weatherford—the Assignee of the present disclosure. The stuffing box 20 fits atop components of a wellhead (not shown), and the sheave assembly 10 attaches to the stuffing box 20 to guide the wireline in and out of the wellhead. The stuffing box 20 has a body 30 with a collar 32 for fitting onto the wellhead. A cartridge insert 36 has glands and packing and positions in the body 30 to pack off the wireline that passes through the stuffing box 20. A packing nut 37 affixes the insert 36 on the body 30, and a hydraulic packing cylinder 34 attaches atop the box 20 and holds a hydraulic packing piston and spring.
As for the sheave assembly 10, side plates 40 connect to a bearing block 38 on the stuffing box's body 30, and a sheave 50 mounted between these plates 40 can rotate about a wheel bearing 52 on an axle 55 disposed between the plates 40. A guard 45 connects by a locking stud 47 to one of the plates 40 so the guard 45 can be removed and adjusted relative to the periphery of the sheave 50.
As best shown in the detail of FIG. 2A, a bush assembly 60 has a bush 70 that fits onto the axle 55 and the side plate 40 on each side of the sheave 50. The bush 70 (shown alone in FIG. 2C) has an opening 75 for the axle 55 and has a shoulder 72 disposed around the bush 70. The sheave 50 can be adjusted using the bush assembly 60 so the assembly 10 can accommodate different sized wirelines. In particular, the bush 70 fits in an upright position in the side plate's opening 42, as indicated by the arrow on the bush 70. The bush's shoulder 72 (FIG. 2C) fits into the side plate's opening 42 (FIG. 2B) so the bush 70 can support the axle 55 in the axle opening 75 (See FIG. 2A).
Depending on how the bush 70 is oriented in the opening 42, a first bush hole 80A on the bush 70 can align with one of two plate holes 61A/62A on the side plate 40. In this way, the screw 90 in first bush hole 80A can fit into the plate hole 61A for 0.187″ wire or can fit into the plate hole 62A for 0.125″ wire. In addition, a second bush hole 80B on the bush 70 can align with one of three plate holes 61B/62B/63B. Here, the screw 90 in second bush hole 80B can fit into the plate hole 61B for 0.108″ wire, can fit into the plate hole 62B for 0.160″ wire, or can fit into the plate hole 63B for 0.250″ wire. Although effective, adjusting the sheave 50 in this way can be tedious and time consuming.
As with the sheave assembly 10 of FIG. 1 and other conventional sheave assemblies of the prior art, a guard is normally attached above the sheave to prevent the wireline from jumping off of the sheave when being run thereon. When rigging up the wireline, the guard must be moved out of the way by removing studs or screws that hold the guard to the assembly. As expected, this procedure can be tedious and time consuming.
In one prior art solution, the assembly supporting the sheave can be entirely hinged out of the way as disclosed in UK Patent Applications GB 2,418,463 and GB 2,433,283 to give access for rigging up the wireline. When such an assembly is hinged out of the way, a cam action lifts the guard clear of the sheave. Because this hinge forms part of the load path of the assembly supporting the sheave, it must be sized in accordance with the safe working load of the stuffing box, which can be disadvantageous.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.